The present invention relates to an error correction system for a position measuring device of the type used to measure the relative position between first and second objects, wherein a measuring scale is coupled to move with the first object and a scanning unit is coupled to move with the second object to scan the scale.
A variety of such error correction systems for position measuring devices are known to the art.
For example, in German Pat. No. 853657, there is described an optical measuring device in which a plate is swingable in a beam path in correspondence to the desired error correction.
In German Pat. No. 27 24 858, a length measuring device is described which includes an error correction system that incorporates a link chain. The individual links of this chain are adjustable transversely with respect to the measuring direction in accordance with the desired error course. A transfer element is provided which scans the link chain and brings about a correcting relative movement in the measuring direction between a scanning unit and a scale included in the measuring device. In the disclosed device, the scanning unit is guided for parallel movement with respect to the division plane of the scale.
German Pat. No. 28 20 753 discloses an error correction system in a length measuring device in which an error correction profile is formed as an integral part of a housing for a scale. This profile is scanned by means of a transfer element and brings about a correcting relative movement in the measuring direction between a scanning unit and a scale included in the measuring device. As above, this scanning unit is guided for parallel movement with respect to the division plane of the scale.
In the correction systems described above, the transfer elements which take the form of swingable angle elements are subject to mechanical wear, and they can result in substantially increased cross-sectional dimensions of the position measuring device. Such an increase in cross-sectional size can be detrimental to a flexible use of the measuring device.